We’ve found the best method of creating a panoramic scene is not to crop the photo during post processing, but to stretch your Second Life Viewer window by clicking on the Restore Down button so that your viewer is no longer maximized, but now is a modal, floating window on your screen.
You should be able to stretch the window by pulling it up from the bottom or down from the top to shrink it vertically until you have your desired panoramic view:
Here is the photo that we got from that shot:
Here is another example taken in another sim.
And yet another: